We develop confidence through experience. We work at something new, get it wrong a bunch of times, learn from each false start, and improve. Eventually we get it right, and our confidence grows.
Another way to gain confidence is to work in a place where people can’t disagree with you.
Once you’ve reached a certain level of authority in any organization you cease to be a practitioner and morph into a manager of practitioners. When you have an idea (good or bad) you aren’t the one to actually execute it: you delegate to your subordinates.
Boss vs Leader
I used the word “manager” above intentionally. In a position of authority, you can either Lead or Demand. Both cause action, but only one invites the person doing the work to commit their best selves to the effort.
And so the second way to gain confidence:
Be a boss, delegate your idea, and blame the practitioner when it doesn’t work (but of course, claim the credit when it does). Some people actually do this to themselves long enough to believe their own mythology. They begin thinking they’re good, when in fact they’re just in charge.
For the rest of us:
Recognize which you’re working for (boss or leader) and adjust your attitude appropriately. Working for a boss? Add the meta goal of learning how to navigate that situation (apply the first paragraph of this post to your interactions with them).